The homeostasis of human pluripotent stem cells (hPSCs) requires the signaling balance of extracellular factors. Exogenous regulators from cell culture medium have been widely reported, but little attention has been paid to the autocrine factor from hPSCs themselves. In this report, we demonstrate that extracellular signal-related kinase 5 (ERK5) regulates endogenous autocrine factors essential for pluripotency and differentiation. ERK5 inhibition leads to erroneous cell fate specification in all lineages even under lineage-specific induction. hPSCs can self-renew under ERK5 inhibition in the presence of fibroblast growth factor 2 (FGF2) and transforming growth factor β (TGF-β), although NANOG expression is partially suppressed. Further analysis demonstrates that ERK5 promotes the expression of autocrine factors such as NODAL, FGF8, and WNT3. The addition of NODAL protein rescues NANOG expression and differentiation phenotypes under ERK5 inhibition. We demonstrate that constitutively active ERK5 pathway allows self-renewal even without essential growth factors FGF2 and TGF-β. This study highlights the essential contribution of autocrine pathways to proper maintenance and differentiation.

Lung cancer is the leading cause of cancer-related deaths worldwide, with non-small cell lung cancer (NSCLC) constituting approximately 84 % of all lung cancer cases. The role of inflammation in the initiation and progression of NSCLC tumors has been the focus of extensive research. Among the various inflammatory mediators, prostaglandin E2 (PGE2) plays a pivotal role in promoting the aggressiveness of epithelial tumors through multiple mechanisms, including the stimulation of growth, evasion of apoptosis, invasion, and induction of angiogenesis. The Extracellular signal-Regulated Kinase 5 (ERK5), the last discovered member among conventional mitogen-activated protein kinases (MAPK), is implicated in cancer-associated inflammation. In this study, we explored whether ERK5 is involved in the process of tumorigenesis induced by PGE2. Using A549 and PC9 NSCLC cell lines, we found that PGE2 triggers the activation of ERK5 via the EP1 receptor. Moreover, both genetic and pharmacological inhibition of ERK5 reduced PGE2-induced proliferation, migration, invasion and stemness of A549 and PC9 cells, indicating that ERK5 plays a critical role in PGE2-induced tumorigenesis. In summary, our study underscores the pivotal role of the PGE2/EP1/ERK5 axis in driving the malignancy of NSCLC cells in vitro. Targeting this axis holds promise as a potential avenue for developing novel therapeutic strategies aimed at controlling the advancement of NSCLC.

Malignant melanoma, an aggressive skin cancer with a poor prognosis, frequently features BRAFV600E mutation resulting in activation of the MAPK pathway and melanocyte proliferation and survival. BRAFV600E inhibitors like vemurafenib and dabrafenib have enhanced patient survival, yet drug resistance remains a significant challenge. We investigated the role of the ERK5 pathway in BRAFV600E melanoma cells and cells with acquired resistance to PLX4720 (vemurafenib) and dabrafenib. In BRAFV600E melanoma, ERK5 inhibition minimally affected viability compared to ERK1/2 inhibition. In vemurafenib-resistant cells, ERK5 inhibition alone didn\'t impact viability or restore drug sensitivity to vemurafenib. However, in dabrafenib-resistant cells, ERK5 inhibition reduced viability and enhanced the anti-proliferative effect of MEK1/2 inhibition. Targeting the ERK5 pathway may represent a therapeutic opportunity in dabrafenib-resistant melanoma.

Extracellular signal-regulated protein kinase 5 (Erk5), a member of the mitogen-activated protein kinase (MAPK) family, is ubiquitously expressed in all eukaryotic cells and is implicated in the various mitotic processes such as cell survival, proliferation, migration, and differentiation. However, the potential functional roles of Erk5 in oocyte meiosis have not been fully determined. In this study, we document that ERK5 participates in the meiotic maturation of mouse oocytes by regulating the spindle assembly to ensure the meiotic progression. We unexpectedly found that phosphorylated ERK5 was localized in the spindle pole region at metaphase I and II stages by immunostaining analysis. Inhibition of ERK5 activity using its specific inhibitor XMD8-92 dramatically reduced the incidence of first polar body extrusion. In addition, inhibition of ERK5 evoked the spindle assembly checkpoint to arrest oocytes at metaphase I stage by impairing the spindle assembly, chromosome alignment and kinetochore-microtubule attachment. Mechanically, over-strengthened microtubule stability was shown to disrupt the microtubule dynamics and thus compromise the spindle assembly in ERK5-inhibited oocytes. Conversely, overexpression of ERK5 caused decreased level of acetylated α-tubulin and spindle defects. Collectively, we conclude that ERK5 plays an important role in the oocyte meiotic maturation by regulating microtubule dynamics and spindle assembly.

Emodin is a naturally occurring anthraquinone derivative with a wide range of pharmacological activities, including neuroprotective and anti-inflammatory activities. We aim to assess the anticancer activity of emodin against hepatocellular carcinoma (HCC) in rat models using the proliferation, invasion, and angiogenesis biomarkers. After induction of HCC, assessment of the liver impairment and the histopathology of liver sections were investigated. Hepatic expression of both mRNA and protein of the oxidative stress biomarkers, HO-1, Nrf2; the mitogenic activation biomarkers, ERK5, PKCδ; the tissue destruction biomarker, ADAMTS4; the tissue homeostasis biomarker, aggregan; the cellular fibrinolytic biomarker, MMP3; and of the cellular angiogenesis biomarker, VEGF were measured. Emodin increased the survival percentage and reduced the number of hepatic nodules compared to the HCC group. Besides, emodin reduced the elevated expression of both mRNA and proteins of all PKC, ERK5, ADAMTS4, MMP3, and VEGF compared with the HCC group. On the other hand, emodin increased the expression of mRNA and proteins of Nrf2, HO-1, and aggrecan compared with the HCC group. Therefore, emodin is a promising anticancer agent against HCC preventing the cancer prognosis and infiltration. It works through many mechanisms of action, such as blocking oxidative stress, proliferation, invasion, and angiogenesis.

OBJECTIVE: Thymic carcinoma is a rare cancer type with limited treatment options. Our previous study demonstrated that statins, which inhibit 3-hydroxy-3-methylglutaryl coenzyme A reductase, can prevent thymic carcinoma. However, the mechanisms through which statins affect intracellular events in cancer cells are not well understood. The aim of the study was to determine how thymic carcinoma modulates the intracellular signals in response to statin administration.
METHODS: We analyzed statin-induced protein phosphorylation in Ty82 human thymic carcinoma cells, which were cultured with fluvastatin, and protein phosphorylation was examined using western blotting.
RESULTS: Treating Ty82 with fluvastatin led to ERK5 phosphorylation via protein prenylation attenuation. The antitumor effects of fluvastatin on thymic carcinoma were enhanced when combined with an ERK5 inhibitor.
CONCLUSIONS: Statin therapy in combination with ERK5 inhibition may be a promising therapeutic approach for treating thymic carcinoma.

Bones are vital for anchoring muscles, tendons, and ligaments, serving as a fundamental element of the human skeletal structure. However, our understanding of bone development mechanisms and the maintenance of bone homeostasis is still limited. Extracellular signal-related kinase 5 (ERK5), a recently identified member of the mitogen-activated protein kinase (MAPK) family, plays a critical role in the pathogenesis and progression of various diseases, especially neoplasms. Recent studies have highlighted ERK5\'s significant role in both bone development and bone-associated pathologies. This review offers a detailed examination of the latest research on ERK5 in different tissues and diseases, with a particular focus on its implications for bone health. It also examines therapeutic strategies and future research avenues targeting ERK5.

Many of the biological processes of the cell, from its structure to signal transduction, involve protein-protein interactions. On this basis, our aim was to identify cellular proteins that interact with ERK5, a serine/threonine protein kinase with a key role in tumor genesis and progression and a promising therapeutic target in many tumor types. Using affinity chromatography, immunoprecipitation, and mass spectrometry techniques, we unveiled an interaction between ERK5 and the mitochondrial glutaminase GLS in pancreatic tumor cells. Subsequent co-immunoprecipitation and immunofluorescence studies supported this interaction in breast and lung tumor cells as well. Genetic approaches using RNA interference techniques and CRISPR/Cas9 technology demonstrated that the loss of ERK5 function led to increased protein levels of GLS isoforms (KGA/GAC) and a concomitant increase in their activity in tumor cells. It is well known that the tumor cell reprograms its intermediary metabolism to meet its increased metabolic needs. In this sense, mitochondrial GLS is involved in the first step of glutamine catabolism, one of the main energy sources in the context of cancer. Our data suggest that ERK5 contributes to the regulation of tumor cell energy metabolism via glutaminolysis.

Castration-resistant prostate cancer (CRPC) is refractory to hormone treatment, and the underlying mechanism has not been fully elucidated. This study aimed to clarify the role and mechanism of Human antigen R (HuR) as a therapeutic target for CRPC progression.
HuR was knocked out by Cas9 or inhibited by the HuR-specific inhibitor KH-3 in CRPC cell lines and in a mouse xenograft model. The effects of HuR inhibition on tumour cell behaviors and signal transduction were examined by proliferation, transwell, and tumour xenograft assays. Posttranscriptional regulation of BCAT1 by HuR was determined by half-life and RIP assays.
HuR knockout attenuated the proliferation, migration, and invasion of PC3 and DU145 cells in vitro and inhibited tumour progression in vivo. Moreover, BCAT1 was a direct target gene of HuR and mediated the oncogenic effect of HuR on CRPC. Mechanistically, HuR directly interacted with BCAT1 mRNA and upregulated BCAT1 expression by increasing the stability and translation of BCAT1, which activated ERK5 signalling. Additionally, the HuR-specific inhibitor KH-3 attenuated CRPC progression by disrupting the HuR-BCAT1 interaction.
We confirmed that the HuR/BCAT1 axis plays a crucial role in CRPC progression and suggest that inhibiting the HuR/BCAT1 axis is a promising therapeutic approach for suppressing CRPC progression.

Metabolic reprogramming in pediatric diffuse midline glioma is driven by gene expression changes induced by the hallmark histone mutation H3K27M, which results in aberrantly permissive activation of oncogenic signaling pathways. Previous studies of diffuse midline glioma with altered H3K27 (DMG-H3K27a) have shown that the RAS pathway, specifically through its downstream kinase, extracellular-signal-related kinase 5 (ERK5), is critical for tumor growth. Further downstream effectors of ERK5 and their role in DMG-H3K27a metabolic reprogramming have not been explored. We establish that ERK5 is a critical regulator of cell proliferation and glycolysis in DMG-H3K27a. We demonstrate that ERK5 mediates glycolysis through activation of transcription factor MEF2A, which subsequently modulates expression of glycolytic enzyme PFKFB3. We show that in vitro and mouse models of DMG-H3K27a are sensitive to the loss of PFKFB3. Multi-targeted drug therapy against the ERK5-PFKFB3 axis, such as with small-molecule inhibitors, may represent a promising therapeutic approach in patients with pediatric diffuse midline glioma.